1. Field of the Invention
This invention relates to a plasma arc torch utilizing a single inlet gas such as air. The torch is intended to be used for cutting metal.
2. Description of the Prior Art
There are believed to be three major United States manufacturers of plasma arc cutting torches, i.e. Thermal Dynamics Corporation of New Hampshire, L-TEC Company of South Carolina, and Hypertherm, Incorporated of New Hampshire. Each of these domestic manufacturers offer a variety of plasma cutting torches some of which have a three-part front-end assembly and some of which have a four-part front-end assembly; the typical four-part front-end assembly consists of the following four separate elements: a nozzle, a tip, a swirl ring, and an electrode. Nomenclature varies from manufacturer to manufacturer; however, the function of the various components is similar. For example, Thermal Dynamics refers to a nozzle as a shield cup; L-TEC refers to the nozzle as a shield and Hypertherm refers to the nozzle as a cap. The term swirl ring is used by Hypertherm; however, the similar element is referred to by Thermal Dynamics as a gas distributor and by L-TEC as a swirl baffle. The term electrode and tip appear to be generally uniform in the industry.
These domestic manufacturers generally arrange the front-end assembly so that the four components stack and nest with each other. This four-component front-end assembly generally screws to the torch head. Worn components can therefore be easily replaced by operators in the field merely by unscrewing the nozzle and replacing one or more of the worn components.
The electrode used by domestic manufacturers is generally an elongated solid pin. The electrode generally has an insert on one or both ends. The elongate electrode typically stacks and nests inside of the hollow swirl ring. The electrode and swirl ring together stack and nest with a tip which forms a recess to receive the elongate electrode. In conventional plasma torches, the electrode, swirl ring and tip nest inside of the nozzle which is screwed on to the torch head. When this four-part assembly is screwed on to the torch head the electrode is forced into electrical contact with a power source which is well known in the plasma cutting art. This conventional four-part front-end assembly is designed for ease of manufacture, for convenience of replacement in the field, and safety.
Because of the high electrical voltages necessary to operate conventional plasma cutting torches, safety of the operator is always a concern. The stacking and nesting arrangement of the front-end assembly is intentionally designed to further ensure the safety of the operator. For example, if the operator takes the front-end assembly apart with the intention of replacing one or more parts and fails to replace the tip and swirl ring, the electrode will typically drop down by the force of gravity into the nozzle and will not be in electrical contact with the power source. If the electrode does not drop down by gravity it will be forced out of contact with the power supply by the force of the inlet gas passing through the head of the torch when the trigger is actuated. If the operator inadvertently touches the front end of a conventional plasma arc cutting torch which has been mis-assembled without the tip and swirl ring, he will not be shocked because the electrode is not in electrical contact with the power source.
However, if the operator merely omits only the tip and reassembles the electrode, the swirl ring and the nozzle, there is a danger of electrocution if the operator inadvertently touches the front end of the torch. When these three of the four components are mis-assembled, the electrode is still in contact with the power source or is close enough to the power source that electricity will arc across a small gap if the trigger is depressed.
The purpose of the present invention is to minimize the possibility of improper assembly in the field which can expose the operator to injury. The present invention focuses on a three-part front-end assembly including (1) an electrode, (2) a tip element with integral swirl ring, and (3) a nozzle. The electrode itself is also thought to be novel in design as well as the tip element with integral swirl ring. The present invention utilizes a parts-in-place concept sometimes referred to in the industry as PIP. The idea is to design the components so that omission of any element during reassembly in the field will deactivate the torch.
The three-part front end assembly of the present invention is safer than the conventional four-part front-end assembly currently used by the major domestic manufacturers of plasma arc cutting torches. If the operator fails to include the tip element with integral swirl ring of the present invention during re-assembly in the field, the electrode will not be in electrical contact with the power supply if the trigger is depressed. The force of the inlet gas passing through the head of the torch will drive the electrode out of electrical contact with the power supply regardless of the orientation of the torch. Inlet gas conventionally operates in excess of 50 psi. When the trigger is depressed, the controller in the power supply first opens the inlet gas to the torch. This inlet gas will therefore arrive first to the torch and blow the electrode out of electrical contact with the power supply. The present invention utilizing a three-part front-end assembly is therefore clearly superior from the standpoint of safety to the conventional four-part front-end assemblies currently used by the major domestic manufacturers. In addition, the electrode design of the present invention is thought to be unique and superior in function to prior art devices. Likewise, the tip element with integral swirl ring is thought to be unique and superior in function to prior art devices.
U.S. Pat. No. 4,590,354 discloses a three-part front-end assembly including an electrode 2, a nozzle 3, and a skirt 4. This patent claims safety as a primary advantage. When this front-end assembly is disassembled, the patent claims that it is safer than the prior art because the conductive element of the torch body is disposed in a hollow part which is difficult to access from the exterior. The patent does not address the issue of safety in the event an operator mis-assembles the torch in the field. For example, if the operator failed to include the tip, referred to in the patent as a nozzle 3, during re-assembly, the electrode would be in electrical contact with the power source and could cause a serious shock if the operator stuck his finger through the end of the nozzle, referred to in the patent as a skirt, into contact with the electrode.
The present invention focuses on the safety of the operator in the event of improper assembly in the field. The present invention also includes an improved design for the electrode and the tip with integral swirl ring. U.S. Pat. No. 4,590,354 does not focus on safety during improper assembly in the field; it focuses on safety when the entire front-end assembly is removed from the torch. The teaching of this prior art is substantially different from the teaching of the present invention.